1. Field of the Invention
One embodiment of the disclosed invention relates to a power storage device.
2. Description of the Related Art
In recent years, environmental destruction is becoming serious around the world and a global-scale solution is required, which increases the importance of establishing and implementing the countermeasures. Consequently, effective use of energy, improvement in energy-saving technology, and development of new technology have been actively promoted at home and abroad by public and private sectors.
In terms of such effective use of energy, improvement in energy-saving technology, and development of new technology, secondary batteries (also referred to as batteries) and power storage devices such as electrochemical capacitors have attracted attention.
As the electrochemical capacitors, for example, an electric double-layer capacitor (EDLC) to which the principle of an electric double layer is applied is known. The electric double layer is a pair of charge layers having opposite polarities, which is formed at the interface between a conductor and an electrolyte solution when the conductor is immersed in the electrolyte solution. An element in which electric energy is physically stored in the electric double layer is an electric double-layer capacitor.
As compared to this electric double-layer capacitor, in a redox capacitor using oxidation and reduction of an electrode active material, oxidation and reduction reactions of an electrode active material can be utilized in addition to the power storage mechanism of the electric double-layer capacitor. Therefore, a redox capacitor has a larger storage capacitance than an electric double-layer capacitor. Another feature of a redox capacitor is to have a higher output than a secondary battery.
Further, an electrochemical capacitor using a solid electrolyte as an electrolyte has also been researched. It is known that, for example, a proton-conducting material (e.g., cesium hydrogen sulfate (CsHSO4), see Patent Document 1), an ionic liquid (see Patent Document 2), or a conductive polymer (see Patent Document 3) is researched to be used as a solid electrolyte. Manufacturing process of such an electrolytic material is complicated, and might require high cost.
[Reference]
[Patent Documents]
    [Patent Document 1] Japanese Published Patent Application No. 2004-247646    [Patent Document 2] PCT International Publication No. WO2005/036573    [Patent Document 3] Japanese Published Patent Application No. 2003-142343